Regioselectivity in free radical bromination of unsymmetrical dimethylated pyridines

During a literature review some curious inconsistencies in the free radical bromination of picolines were noted. To achieve a better understanding of the mechanisms and regioselectivity we reran these reactions, extending our work to unsymmetrical lutidines using N-bromosuccinimide in limiting amount. Characterization of the products was done with GC/MS and H NMR. The regioselectivity of bromination in unsymmetrical dimethylpyridines shows that nitrogen in the ring is deactivating inductively. The competition between 2,3, 2,4, and 2,5 dimethyl pyridine toward bromination results with bromination in the methyl group farthest from the N in the ring. 3,4-Lutidine shows only the 4,4-dibrominated product.

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